The Massachusetts Historical Commission is reviewing an application — already approved by the Board of Selectmen — that would preserve the historic touches of the 1872 Fletcher Building, at 49 Main St. Renovations of the four-story building were completed last September at a cost of $1.3 million. The work was done by Senate Construction Corp. of Shirley. Six apartments are now rented and one of two retail spaces is occupied, said Robert France, chief executive officer of Senate Construction and co-owner of the building.